It is known that the vibration of a ski can represent a significant disadvantage to the skier, not only because such vibration generates sounds which are annoying and may limit the control that a skier has on the skiing action, but because the vibration is a significant factor in the tiring of the skier.
For this reason it has been proposed heretofore to provide a ski damper (see German patent document DE-A 2,747,084) in which an oscillating mass is disposed in a polymeric foam filling a space containing the damper on a ski.
Other damping devices for vibration have been provided heretofore, although not necessarily in conjunction with skiis, wherein an oscillating mass is provided in conjunction with a damping mass of elastomeric material. Reference may be had, for example, to German patent document DE-B 1,249,018.
Furthermore, in German patent document DE-A 1,478,110 and in U.S. Pat. No. 4,018,454, damper structures are described for ski vibration which also utilize the principle of absorption of oscillating energy.
Surprisingly, none of the documents mentioned, nor any others relating to the damping of ski vibrations, to the best of our knowledge, deals with the dimensioning or the specific structural configurations of a damper to damp the particular range of frequencies to which the present invention is specifically directed. Presumably, since it is known that the modes of vibration of a ski are numerous and complex, the approach generally has been in the past to accept any frequency attenuation in the range of several Hz to several thousands Hz which may be generated in the ski.
In other words, it presumably has been acceptable heretofore to disregard the limited range of frequencies for which attenuation was possible with any single vibration damper heretofore because to do otherwise would require the application of a number of absorbers of different types for a given ski, something which is unacceptable because of the resulting interference with the skiing action.
Thus it has not been possible heretofore to obtain a total damping over the entire range of frequencies and this has created the problem of selection of the frequency to be attenuated.
These efforts have developed in two directions. On the one hand, there have been suggestions as to the damping of low frequency vibrations, generally vibrations below about 50 Hz, utilizing oscillating bodies of the type described previously. The second approach has been that of modifying the composition of the ski or the structure of the ski itself to enable the absorption of relatively high frequencies, generally frequencies of about 500 Hz and higher. The damping of the low frequency vibrations require comparatively heavy and large unit and to the extent to which benefit is obtained by damping these low frequency vibrations, there is a comparable degree of inconvenience resulting from the size in mass of the damping unit which is required. The damping of relatively high frequencies is obtained by an appropriate choice of the material used in constructing the ski and by the mode of fabrication. Mention may also be made of the fact that it is the low frequency vibrations which are most noticeable and even perceptible to the eye and the ones which are most strongly attenuated by contact of the ski with the snow.
Until now there has been no satisfactory solution to the problem of intermediate frequency vibrations, namely, vibrations in the range of 100 to about 500 Hz.
We have discovered, quite surprisingly, that these vibrations appear to be amplified by contact of the ski with the snow, especially during braking or turning.
This particular range of vibrational frequencies, moreover tend to reduce the purchase of the ski on the snow, especially when the snow is hard, and on ice, thereby interfering with the precision with which the ski can be guided and the control which the skier has of the skiing operation. Since greater muscular effort is required to maintain the ski in its direction of travel, this vibrational frequency range contributes to the exhaustion of the skier.
Indeed, we have found that one of the significant failures of earlier damping approaches to ski vibrations has been the inability to deal with the vibrations in the middle frequency range between 100 to 500 Hz and the lack of any significant contribution to the solution of the problem over the last 20 years or more since the vibration problem was first considered.